Fix a typo, a conflict and improve documentation

app/models/namespace.rb

@@ -222,7 +222,7 @@ class Namespace < ActiveRecord::Base
     has_parent?
   end
 
-  # Overriden on EE module
+  # Overridden on EE module
   def multiple_issue_boards_available?
     false
   end

config/routes/project.rb

@@ -381,6 +381,7 @@ constraints(ProjectUrlConstrainer.new) do
 
       get 'noteable/:target_type/:target_id/notes' => 'notes#index', as: 'noteable_notes'
 
+      # On CE only index and show are needed
       resources :boards, only: [:index, :show]
 
       resources :todos, only: [:create]

doc/user/project/issue_board.md

@@ -237,6 +237,8 @@ Issue Board, that is create/delete lists and drag issues around.
 
 ##  Group Issue Board
 
+>Introduced in GitLab 10.6
+
 Group issue board is analogous to project-level issue board and it is accessible at the group
 navigation level. A group-level issue board allows you to view all issues from all projects in that group
 (currently, it does not see issues from projects in subgroups). Similarly, you can only filter by group labels for these